Built-up rotor construction for rotary mechanisms

ABSTRACT

The built-up rotor comprises a plurality of rotor components produced by stamping and cutting sheet metal material and bonding together such components into a unitary assembly. A plurality of flank components of the rotor are disposed between the inner side faces of the side walls and are supported by radially extending spaced flange portions of a bearing hub component. Additional support of the flanks is provided by a single reinforcing plate mounted on the bearing hub and projecting radially so as to engage the inner surfaces of the flanks. This construction provides the rotor with the strength and stability necessary to resist deformation and thereby maintain the continuity of the bonded joints and the leakproof character of the rotor under the cyclically varying loads and thermally induced stresses to which the rotor is subjected during use.

' United States Patent 1191 A Wieland 5] Nov. 18, 1975 BUILT-UP ROTOR CONSTRUCTION FOR 3,299,862 1/1967 Peras 418/91 ROTARY MECHANISMS 3,302,624 2/1967 Tatsut0mi.... 418/91 3,799,706 3/1974 B1lobran., 418/61 A [75] Inventor: Werner Wieland, Obereisesheim, 1 1 Germany Primary Examiner.l0hn J. Vrablik [73] Assignees: Audi NSU Auto U i Attorney, Agent, or Firm-Arthur Frederick; Victor D.

Aktiengesellschaft, Neckar sulm; Behn Wankel G.m.b.H., Lindau, Bondensee, both of Germany [57] ABSTRACT [22 i Oct 25 974 The built-up rotor comprises a plurality of rotor components produced by stampmg and cutting sheet metal [21] APPI' N04 517,966 material and bonding together such components into a unitary assembly. A plurality of flank components of 30 Foreign Application priority Data the rotor are disposed between the inner side faces of Nov 8 1973 German 2355738 the s1de walls and are supported by rad1ally extendmg y spaced flange portions of a bearing hub component. [52 US. Cl. 418/61 A; 418/91; 29/1565 R 9 2 1 i j l 2 51 Int. 01. F01C 1/02; F04C 17/02; 1323? 15/10 F a e 6 on e eafmg u [58] Field of 8 ch 418/61 A 123/8 Jectmg rad1ally so as to engage the inner surfaces of i H5615 the flanks. This construction provides the rotor with the strength and stability necessary to resist deformation and thereby maintain the continuity of the [56] References cued bonded joints and the leakproof character of the rotor UNITED STATES PATENTS under the cyclically varying loads and thermally inl,293,916 2/1919 Pribil 29/1565 R duced stresses to which the rotor is subjected during 1,854,455 4/1932 Day 29/1565 R use 2,341,836 2/1944 Wood 29/1565 R 3,059,585 10/1962 Froede et a] 418/61 A 11 Clalms, 6 Drawmg g s Z&% I 1 420 I 1 -4i JZ /a A 1 11 T/ s 7 2%ZJ 2 4 6 0: 1 J

US. Patent Nov. 18, 1975' Sheet 1 of2 Illlll IHII Nov. 18, 1975 Sheet 2 of 2 Patent BUILT-UP ROTOR CONSTRUCTION FOR ROTARY MECHANISMS This invention relates to rotors of rotary mechanisms of the Wankel et al, type disclosed in U.S. Pat. No. 2,988,065 and, more particularly, to the structure and the method of construction of lightweight rotors of the type produced by bonding together rotor components of sheet metal material. Still more specifically, the invention is an improvement in the lightweight rotors of the type disclosed in applicants copending U.S. patent application, Ser. No. 423,159, filed Dec. 10, 1973 Now U.S. Pat. No. 3,877,849.

In the lightweight or built-up rotors produced by bonding together a plurality of rotor components formed from sheet metal material by stamping and cutting, the welded or soldered joints, particularly such joints between the flank components and the side wall elements, may open under the cyclically variable loads and thermal stresses tending to deform the rotor. This opening of such joints is undesirable since it causes leakage of cooling fluid passing through the rotor from the rotor into the working chambers and working fluid from the working chambers defined by the rotor and the trochoidal shaped housing cavity within which the rotor planetates. It is, therefore, of importance in a' lightweight, multi-component rotor, that it have the requisite strength and stability to resist deformation and maintain the leakproof character of the rotor bonded joints under the loads and thermal stresses to which the rotor is subjected in use.

It is therefore an object of this invention to provid an improved built-up rotor construction wherein the component parts are bonded together into a unitary assembly, which is tighter and stronger than heretofore known built-up rotors.

Another object of the present invention is to provide an improved built-up rotor construction wherein the integrity of the bonded joints is maintained in spite of the loads and thermally induced stresses to which the rotor is subjected when in use.

SUMMARY OF THE INVENTION Accordingly, the present invention contemplates an improved built-up rotor for rotary mechanisms of the Wankel type and an improved method of fabrication of such rotors. The built-up rotor of this invention comprises a plurality of component elements cut and formed of sheet metal material bonded together into a unitary, relatively lightweight structure, the component elements being so formed and, sized relative to each other that the unitary rotor structure has the strength and stability to resist deformation and the consequent rupture of the bonded joints under the cyclically varying loads and thermally induced stresses to which the rotor is subjected during use.

More specifically, the improvement according to this invention comprises a bearing hub having a hub portion and axially spaced, radially extending, flange portions, which bearing hub is fabricated from two halves joined together at the abutting hub regions. The flange portions are dimensioned so that their outer peripheral 1 edge portions are spaced radially inwardly of the outer peripheral surfaces of the two congruent side wall elements which are positioned in abutment against the outer faces of the flange portions of the bearing hub. The step or shoulder thus formed by the flange portions and side walls receive and support the opposite elongated side edge portions of each of a plurality of flank elements. To provide additional support to each of the flank elements, particularly in the region of the pockets or recesses formed in the outer surfaces of the flank elements, a reinforcing plate surrounds the bearing hub and projects radially therefrom to engage the inner surfaces of each of the flank elements. The support of the flank elements of the flanges of the bearing hub and the reinforcing plate enables the rotor in use to resist the cyclically varying forces and thermally induced stresses so that the integrity of the rotor shape and bonded joints is maintained.

A further increase in structural strength is provided the rotor of this invention by interconnecting adjacent end portions of the flank elements with connecting I pieces or members, each of which connecting pieces is formed to define with the inner surfaces of the associated flank elements an opening for receiving a piece of bar stock material. The bar stock is suitably machined to provide support for apex seal assemblies.

As is conventional, the bearing hub adjacent each of the flange portions is provided with a plurality of circumferentially spaced openings. One set of openings serving as cooling liquid inlet openings while the other set of openings serve as cooling liquid outlet openings. To direct the liquid flowing into the inlet openings, the reinforcing plate is provided with tabs equal in number to the number of inlet openings so that there is one for each inlet opening. Each of the tabs is shaped and sized to project axially with a portion thereof extending into the center of an associated inlet hole and in abutment with the bearing hub and the inner surface of the adjacent flank element'. The tabs serve to further strengthen the flank elements as well as serve as a partition or baffle to split the cooling liquid into oppositely directed circumferential streams.

Each of the side wall elements are positioned relative to the bearing hub by pilot means. The pilot means, according to one embodiment of the invention, is a plurality of dowels, each of which is receivable in aligned holes in each of the side wall elements and abutting flange portion of the bearing hub. In another embodiment, the dowel means consists of a plurality of pins which extend through aligned openings in each of the flange portions and side wall elements. Each pin extends from one side wall element to the other and is provided at opposite ends with axial recesses so that the ends can be readily expanded. In a still further embodiment, the pilot means is a plurality of protuberances projecting from one side of each of the side wall elements, each of the protuberances, which may be produced by haIf-punched-through incisions pressed out of the side wall elements, being dimensioned to project into and closely fit within an associated hole in the adjacent flange portion of the bearing hub.

The method of fabrication according to this invention of the built-up rotor of this invention comprises the steps of securing, as by welding, the connecting pieces to the end portions of the flank elements to form a closed structure and securing and reinforcing plate to a first half portion of the bearing hub with the tabs positioned to extend into the inlet openings. Thereafter, the other half of the bearing hub is placed in abutment at its hub region against the hub region of the first half portion and the halves secured together at the line of abutment. The bearing hub and reinforcing plate subassembly is then positioned within the closed structure formed by the interconnected flank elements so that a 3 welding gap of 0.3 mm, at most, and, preferably, of 0.2 mm is provided at the side edge portions of each of the flank elements and the peripheral edge portions of the flange portions. The flank elements along their side edge portions are bonded, as by tack welding, to the flange portions of the bearing hub. Thereafter, the outer surfaces of the flange portions and the side edge portions of the flank elements are ground to provide a continuous flat surface. Following grinding, each side wall element is coated with a bonding material, such as a soldering paste, and set against the flange portion of the bearing hub, the pilot means being utilized to properly orientate the side wall elements. The entire assembly is then bonded together.

The fabrication method above described has the advantage that the side wall elements are assembled in accurate parallelism and that an extremely small gap between the components results so that minimal bonding medium is used with improved flowing and setting characteristics. This results in leakproof bonded joints of high strength.

The method contemplates, in addition to bonding the rotor assembly together by use of soldering paste, in the alternative after tack-welding the abutting side wall elements to the bearing hub and flank elements subassembly, galvanically coppering the assembly. By the latter process, the copper in the heating oven liquifies and is drawn by capillary action into the gaps between the components of the rotor assembly. This coats the entire inner surfaces of the rotor assembly with a thin layer of copper thereby inhibiting corrosion by the cooling liquid.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following description when considered in connection with the accompanying drawings, in which:

FIG. 1 is a side elevational view of the rotor according to this invention with parts broken away for illustration purposes;

FIG. 2 is a cross-sectional view taken substantially along line 22 of FIG. 1;

FIG. 3 is a fragmentary view in cross-section similar to a portion of FIG. 2 showing an alternative pilot means according to this invention;

FIG. 4 is a top plan view of the rotor shown in FIG. 1 with parts broken away for purposes of illustration;

FIG. 5 is a view similar to FIG. 3 showing another alternative pilot means; and

FIG. 6 is an exploded view in perspective of the rotor components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to the drawings, and more specifically FIGS. 1, 2, 4 and 6, the reference number 10 generally designates the built-up rotor according to this invention. The rotor is of the type employed in rotary mechanisms of the kind disclosed in the U.S. patent to Wankel et al., U.S. No. 2,988,065 and of the type built-up from individual components or elements rather than of the integrally cast type. It is an improvement over the built-up rotor and method of manufacture thereof disclosed in applicants copending U.S. patent application, Ser. No. 423,159, filed Dec. 10, 1973 now us. Pat. No. 3,877,849.

The rotor 10 comprises a bearing hub 12, a plurality of contiguous, interconnected flank elements 14, a re- 4 inforcing plate 16 and two congruently shaped side wall elements 18 and 20 all of which components are produced by dimensionally accurate stamping and cutting of sheet metal material.

The bearing hub 12 comprises two joined, essentially mirrorimage parts, each of which has a tubular hub portion 26 and an integral, radially extending flange portion 28. The flange portions 28 are dimensioned so that their peripheral edge portions are inwardly spaced from the peripheral edges of side wall elements 18 and 20 to form a shoulder 30 against which the inner surface of the side edge portions of flank elements 14 abut. The bearing hub adjacent one of the flange portions 28 is provided with a plurality of circumferentially spaced coolant inlet openings 32, while adjacent the other flange portion 28, a plurality of circumferentially spaced coolant outlet openings 34 are provided.

The reinforcing plate 16 is provided with a central opening 36 to receive therein the tubular hub portions 26 of the bearing hub and thus be in a plane extending normal to the axis of bearing hub 12. Also, reinforcing plate 16 has peripheral edge portions 38 dimensioned and shaped to conform to and be secured to the inner surfaces 40 of flank elements 14 along a substantially central, longitudinal line of the flank elements. For purposes of weight reduction and passage of cooling liquid, the reinforcing plate is provided with arcuate shaped peripheral edge surfaces 42 between each of the edge portions 38. The reinforcing plate 16 thus supports each of the flank elements 14 and lends rigidity to the built-up rotor 10. To provide added support of flank elements 14, the reinforcing plate is provided with a plurality of tabs 44. Each of the tabs 44 may be L shaped elements which are tack welded to one of the faces of reinforcing plate 16 (see FIG. 4) and with a portion 46 extending in a plane substantially normal to the face of the reinforcing plate and substantially parallel to the axis of bearing hub 12 (see FIG. 2). Each of the tab portions 46 is dimensioned and shaped to abut the inner surfaces of flank elements 14, hub portion 26 of bearing hub 12 and end wall 20. So that tab portions 46 may serve an additional function to their reinforcing function, each tab portion 46 is preferably dimensioned and shaped to, at least partially, extend at 46A into a coolant inlet opening 32 (see FIGS. 2 and 4). The tab portions 46 thereby serve as baffles to split the cooling liquid flow entering each of the inlet openings 32 into two oppositely directed circumferential streams as shown by arrows A in FIG. 1. This coaction of tab portions 46 and inlet openings 32 also functions, during assembly, to properly position reinforcing plate 16 relative to bearing hub 12. The cooling liquid, which is diverted by tab portions 46 toward the apex portions of the rotor, flows over arcuate edge surfaces 42 into the chamber formed on the opposite side of the reinforcing plate and, thence, out of outlet openings 34.

To further strengthen the rotor and, more particularly, flank elements 14, the flank elements 14 are interconnected by connecting pieces 48. Each connecting piece 48 has an arcuate shaped portion 50 and tab portions 52 which abut and are secured to the inner surfaces 40 of the adjacent flank elements to be connected together. The curved portion 50 is dimensioned to snugly receive therein a bar stock member 54 from which are machined the necessary grooves and recesses (not shown) for receiving and supporting an apex seal assembly (not shown).

The side wall elements 18 and 20 have a central opening 56 of a size substantially thatof the internal diameter of tubular portions 26 of bearing hub..l2. One of the side wall elements, such as side wall element 20, as shown, may be made of hardenable steel and provided with an internal timing gear 58. The inner faces of side wall elements 18 and 2 abut the outer surfaces of flange portions 28 of bearing hub 12. To position each of the side wall elements 18 and 20 in a desired relationship to the bearing hub, a plurality of pilot pins 60 are positioned inaxially aligned holes 62 and 64 in each side wall 18 and 20 and on adjacent flange portion 28 of bearing hub 12.

In FIG. 3 is shown a first alternative pilot means consisting of dowels 66 extending from one side wall element to the other through axially aligned holes in side wall elements 18 and 20 and flange portions 28 of bearing hub 12. The opposite ends of each dowel 66 is provided with recesses 68 to facilitate expansion of the end portions of the dowels and thereby provide a very narrow bonding gap.

In FIG. 5 is illustrated a second' alternative pilot means which comprises a hole 70 in flange portions 28 of bearing hub 12 into which snugly fits a protuberance 72 projecting from the inner surface of the adjacent side wall element. The protuberances 72 may be formed by half-stamped-through incisions pressed out of the side wall elements. i

All of the component parts of rotor '10 are for the most part bonded together 'by soldering into unitary structure. This assembly method according to this invention comprises the first step of placing the piston flanks 14 in a jig or holding device so that the end portions thereof are in close spaced relation to each other and securing the connecting pieces 48 to the adjacent end portions along the inner surfaces 40 of flank elements 14. The reinforcing plate 16 is positioned over and secured to tubular portion 26 of the half of bearing hub 12 containing the coolant inlet openings 32 so that each of the tabs 44 engage, at 46A, openings 32. The other half of bearing hub 12 is secured at the end of its tubular hub portion to the end of the tubular hub portion 26 of the half to which reinforcing plate 16 is secured. This subassembly of reinforcing plate 16 and bearing hub 12 is positioned within the closed structure formed by the interconnected flank elements 14 and while keeping a soldering gap of, for example 0.2 mm to about 0.05 mm, the components are fastened together by spot-welding along the longitudinal side edges of the flank elements and the shoulders 30. Thereafter, the outer faces of flange portions 28 and the associated side edges of the flank elements are ground flat to form common plane surfaces. The two opposite surfaces are also ground so that they are in substantial parallelism. Then, at the abutment joints and the outer faces of flange portions 28 a soldering medium in paste form is applied. The soldering medium is preferably copper solder with a nickel additive. The two side wall elements 18 and 20 are set in place against the outer surfaces of flange portions 26 and properly positioned by the pilot means, such as pins 52, dowels 60 or protuberances 72. This prepared and assembled rotor is then placed in a heating chamber or oven, where at a temperature of about 1 100C all of the component elements of the rotor are tightly bonded together.

Following the bonding of rotor 10 into a unitary assembly, the internal timing gear 58 is hardened in a 6 suitable manner such as by high-frequency method, and the internal surface of bearing hub 12, the gear teeth and the grooves (not shown) and recesses (not shown) for the apex seal assemblies are machine finished by conventional machines and methods.

It is believed now readily apparent that the present invention provides an improved built-up rotor and method of fabrication thereof having the requisite strength and stability to resist deformation under the cyclical loads and thermally induced stresses acting on the rotor in use so that the continuity and integrity of the bonded joints is maintained Although but one embodiment of the invention has been'illustrated and described in detail, it is to be ex pressly understood that the invention is not limited thereto. Various changes can be made in the arrangement of parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. A rotor having a plurality of component elements of cut and formed sheet metal material and bonded together into a unitary structure and disposed for eccentric rotation within a housing cavity partially defined by a trochoidal peripheral surface, the rotor comprising:

'a. at least one element forming a bearing hub having axially spaced, radially extending flange portions;

b. two substantially congruent side wall elements disposed on opposite sides of the bearing hub and in abutment against said flange portions;

c. said bearing hub flange portions being dimensioned so that their outer peripheral edges thereof are spaced inwardly of the outer peripheral edges of the side wall elements; and

cl. a plurality of flank elements each of which have inner and outer surfaces, opposite side edge portions and opposite end edge portions;

e. the flank elements being disposed with their said inner surfaces secured to the outer peripheral edge portions of said flange portions of the bearing hub and with their opposite side edge portions secured against said side wall elements so that the outer surfaces of the flank elements lie substantially flush with the outer peripheral edges of the side wall elements.

2. The apparatus of claim 1 wherein a single reinforcing plate is disposed on the bearing hub to extend substantially parallel to the side wall elements and dimensioned and formed to abut the center portions of the inner surfaces of the flank elements.

3. The apparatus of claim 2 wherein said bearing hub is provided with circumferentially spaced coolant inlet holes adjacent one flange portion thereof and circumferentially spaced coolant outlet holes adjacent the other flange portion thereof and wherein said plate has an axially extending guide tab for each coolant inlet hole so dimensioned and formed to project into its associated inlet hole to divide the flow area thereof.

4. The apparatus of claim 1 wherein pilot means is provided for positioning each of the side wall elements relative to the bearing hub.

5. The apparatus of claim 4 wherein said pilot means comprises a plurality of dowels each of which is receivable in aligned holes in each of the side walls and the abutting flange portion of the bearing hub.

6. The apparatus of claim 4 wherein said pilot means is a plurality of pins each of which extend through aligned openings in the side wall elements and the 7 flange portions, each of said pins being provided with axial recesses in the ends thereof to permit expansion of said pins in the associated openings in the side wall elements.

7. The apparatus of claim 4 wherein said pilot means comprises a plurality of protuberances projecting from each side wall element each of said protuberances projects into an associated hole in the abutting flange portion of the bearing hub.

8. The apparatus of claim 1 wherein each of the end edges of next adjacent flank elements are interconnected by a connecting plate formed to define with the associated flank element an opening and wherein a bar element is receivable in each of such openings.

9. The method of fabricating a rotor having two spaced side wall elements interconnecting at their periphery by a plurality of contiguous converging flank portions, the rotor being for use in a rotary mechanism of the type having a rotor cavity partially defined by a trochoidal peripheral surface, the method comprising the steps of:

a. forming by stamping and cutting a bearing hub from relatively thin sheet metal material and having spaced substantially parallel flange portions;

b. forming by stamping and cutting relatively thin sheet metal material to form two substantially congruent side wall elements having a plurality of converging edge surfaces;

c. forming by stamping and cutting from relatively thin sheet metal material a plurality of flank elements corresponding in number to the number of 8 edge surfaces of each of the side wall elements and having opposite side edges;

d. cutting solid metal inserts from bar stock material to the length required to extend between the side wall elements at each of the points of convergence of the flank elements;

e. cutting and forming relatively thin sheet metal material to form connecting plates for connecting the flank elements at their convergence;

f. cutting and forming relatively thin sheet metal material to form a reinforcing plate and attaching guide tabs to the latter also cut and formed from relatively thin sheet metal material;

g. welding the connecting plates to the flank elements;

h. placing the reinforcing plate around the bearing hub and disposing this assembly in between the connected together flank elements;

i. the flank elements, reinforcing plate and said bearing hub are then spot welded together;

.j. the flange portions of the bearing hub and the side edges of the flank elements are ground flat to form a common plane; and v k. surfaces of each of the side wall elements are set against the common plane and the elements bonded into a unitary assembly.

10. The method of claim 9 wherein said elements are soldered together into a unitary assembly.

11. The method of claim 9 wherein said elements are galvanically coppered. 

1. A rotor having a plurality of component elements of cut and formed sheet metal material and bonded together into a unitary structure and disposed for eccentric rotation within a housing cavity partially defined by a trochoidal peripheral surface, the rotor comprising: a. at least one element forming a bearing hub having axially spaced, radially extending flange portions; b. two substantially congruent side wall elements disposed on opposite sides of the bearing hub and in abutment against said flange portions; c. said bearing hub flange portions being dimensioned so that their outer peripheral edges thereof are spaced inwardly of the outer peripheral edges of the side wall elements; and d. a plurality of flank elements each of which have inner and outer surfaces, opposite side edge portions and opposite end edge portions; e. the flank elements being disposed with their said inner surfaces secured to the outer peripheral edge portions of said flange portions of the bearing hub and with their opposite side edge portions secured against said side wall elements so that the outer surfaces of the flank elements lie substantially flush with the outer peripheral edges of the side wall elements.
 2. The apparatus of claim 1 wherein a single reinforcing plate is disposed on the bearing hub to extend substantially parallel to the side wall elements and dimensioned and formed to abut the center portions of the inner surfaces of the flank elements.
 3. The apparatus of claim 2 wherein said bearing hub is provided with circumferentially spaced coolant inlet holes adjacent one flange portion thereof and circumferentially spaced coolant outlet holes adjacent the other flange portion thereof and wherein said plate has an axially extending guide tab for each coolant inlet hole so dimensioned and formed to project into its associated inlet hole to divide the flow area thereof.
 4. The apparatus of claim 1 wherein pilot means is provided for positioning each of the side wall elements relative to the bearing hub.
 5. The apparatus of claim 4 wherein said pilot means comprises a plurality of dowels each of which is receivable in aligned holes in each of the side walls and the abutting flange portion of the bearing hub.
 6. The apparatus of claim 4 wherein said pilot means is a plurality of pins each of which extend through aligned openings in the side wall elements and the flange portions, each of said pins being provided with axial recesses in the ends thereof to permit expansion of said pins in the associated openings in the side wall elements.
 7. The apparatus of claim 4 wherein said pilot means comprises a plurality of protuberances projecting from each side wall element each of said protuberances projects into an associated hole in the abutting flange portion of the bearing hub.
 8. The apparatus of claim 1 wherein each of the end edges of next adjacent flank elements are interconnected by a connecting plate formed to define with the associated flank element an opening and wherein a bar element is receivable in each of such openings.
 9. The method of fabricating a rotor having two spaced side wall elements interconnecting at their periphery by a plurality of contiguous converging flank portions, the rotor being for use in a rotary mechanism of the type having a rotor cavity partially defined by a trochoidal peripheral surface, the method comprising the steps of: a. forming by stamping and cutting a bearing hub from relatively thin sheet metal material and having spaced substantially parallel flange portions; b. forming by stamping and cutting relatively thin sheet metal material to form two substantially congruent side wall elements having a plurality of converging edge surfaces; c. forming by stamping and cutting from relatively thin sheet metal material a plurality of flank elements corresponding in number to the number of edge surfaces of each of the side wall elements and having opposite side edges; d. cuttinG solid metal inserts from bar stock material to the length required to extend between the side wall elements at each of the points of convergence of the flank elements; e. cutting and forming relatively thin sheet metal material to form connecting plates for connecting the flank elements at their convergence; f. cutting and forming relatively thin sheet metal material to form a reinforcing plate and attaching guide tabs to the latter also cut and formed from relatively thin sheet metal material; g. welding the connecting plates to the flank elements; h. placing the reinforcing plate around the bearing hub and disposing this assembly in between the connected together flank elements; i. the flank elements, reinforcing plate and said bearing hub are then spot welded together; j. the flange portions of the bearing hub and the side edges of the flank elements are ground flat to form a common plane; and k. surfaces of each of the side wall elements are set against the common plane and the elements bonded into a unitary assembly.
 10. The method of claim 9 wherein said elements are soldered together into a unitary assembly.
 11. The method of claim 9 wherein said elements are galvanically coppered. 